1. Field of the Invention
The present invention relates to braking system.
2. Discussion of Related Art
Japanese Patent Application No. 2000-174029, which was filed by the assignee of the present application and which has not been laid open at the time the present invention was made, discloses an example of a braking system including (a) a power-operated hydraulic pressure source operable to deliver a pressurized working fluid, (b) a brake including a brake cylinder and operated by activation of the brake cylinder with the pressurized fluid supplied thereto, and (c) a hydraulic pressure control device disposed between the power-operated hydraulic pressure source and said brake cylinder, and operable to control the pressure of the pressurized fluid delivered from the hydraulic pressure source, for thereby controlling the pressure of the pressurized fluid in said brake cylinder. In this braking system, the pressure control device includes a master cylinder which is disposed between the hydraulic pressure source and the brake cylinder and which includes a pressurizing piston operatively connected to a manually operable brake operating member. The pressurizing piston partially defines a front pressurizing chamber on a front side thereof. The fluid in the pressurizing chamber is pressurized as the pressurizing piston is advanced, so that the brake cylinder is activated with the pressurized fluid delivered from the pressurizing chamber, whereby the brake is operated.
In the braking system described above, the fluid pressure in a rear pressure chamber formed on the rear side of the pressurizing piston is controlled on the basis of the pressurized fluid delivered from the power-operated hydraulic pressure source. The pressurizing piston receives an operating force of the brake operating member and an assisting force based on the fluid pressure in the rear pressure chamber, so that the pressurizing piston is advanced by a sum of the operating force of the brake operating member and the assisting force. By controlling the fluid pressure in the rear pressure chamber, a relationship between the brake operating force and the fluid pressure in the pressurizing chamber, namely, a relationship between the brake operating force and the braking pressure is controlled.
In the braking system indicated above, the flows of the fluid into and from the pressurizing chamber of the master cylinder are controlled. More specifically described, the pressurized fluid delivered from the power-operated hydraulic pressure source is fed into the pressurizing chamber, or the pressurized fluid is discharged from the pressurizing chamber to a reservoir, so that a relationship between an operating stroke of the brake operating member and the pressure of the fluid in the pressurizing chamber, namely, a relationship between the operating stroke and the braking pressure in the brake cylinder is controlled.
Thus, not only the relationship between the brake operating force and the braking pressure but also the relationship between the operating stroke and the braking pressure are controlled in the braking system described above.